In various optical systems, the frequency of converting (collimating) diverging light emitted from a point light source (including a light source regarded as the point light source) into parallel light is high. As examples of the point light source, there are a laser diode and an optical fiber emission end. A distance between the point light source and a collimation optical system is appropriately set, so that the diverging light emitted from the point light source can be converted into the parallel light by the collimation optical system. Technologies for evaluating a degree of parallelization (degree of collimation) of the parallel light generated as described above are described in Patent Documents 1 and 2.
In particular, according to the technology described in Patent Document 1, collimation of light can be easily evaluated using a shear plate having a first reflection surface and a second reflection surface which are non-parallel to each other. That is, a collimation evaluation device using the shear plate causes light reflected on the first reflection surface of the shear plate and light transmitted through the first reflection surface of the shear plate and being reflected on the second reflection surface to interfere with each other on a screen, and can evaluate collimation of the light on the basis of a direction of interference fringes on the screen. The shear plate may be called a shearing plate.